Methods and apparatuses for resource management in a multi-carrier telecommunications system

ABSTRACT

The embodiments of the present invention relate to apparatuses and methods for resource management in a multi-carrier system wherein a plurality of component carriers (CCs) is defined per cell. According to a method in an apparatus corresponding to a radio base station, a message is assembled comprising information on the structure of the cell served by the radio base station; the information including one or more CCs used in the cell that is/are available for a user equipment for performing initial access in the cell. The method also comprises, transmitting the assembled message to the user equipment and indicating to the user equipment to what resources to use for random access in the cell. The exemplary embodiments of the present invention also relates to a method in the user equipment, to a radio base station and to a user equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/767,959 filed on Apr. 27, 2010, which claims benefit of U.S.Provisional Application No. 61/172,813, filed Apr. 27, 2009, andInternational Application No. PCT/SE2009/050945, filed Aug. 21, 2009,the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of wirelesstelecommunications, and, more particularly, to methods and apparatusesfor resource managements for devices operating in a multi-carrier systeme.g. the LTE-advanced (Long Term Evolution) system.

The 3rd Generation Partnership Project (3GPP) is responsible for thestandardization of the UMTS (Universal Mobile Telecommunication Service)system, and LTE is currently under discussion as a next generationmobile communication system of the UMTS system. LTE is a technology forrealizing high-speed packet-based communication that can reach high datarates both in the downlink and in the uplink. The 3GPP work on LTE isalso referred to as Evolved Universal Terrestrial Access Network(E-UTRAN). Thus work is ongoing in 3GPP to specify an evolution toUTRAN, denoted E-UTRA, as part of the LTE effort. The first release ofLTE, referred to as release-8 (Rel-8) can provide peak rates of 300Mbps, a radio-network delay of e.g. 5 ms or less, a significant increasein spectrum efficiency and a network architecture designed to simplifynetwork operation, reduce cost, etc. In order to support high datarates, LTE allows for a system bandwidth of up to 20 MHz. LTE is alsoable to operate in different frequency bands and can operate in at leastfrequency division duplex (FDD) and time division duplex (TDD). Otheroperation modes can also be used. It should be noted that OFDM(orthogonal frequency division multiplexing) is supported in LTE.

For the next generation mobile communications system e.g. IMT-advancedand/or LTE-advanced, which is an evolution of LTE, support forbandwidths of up to 100 MHz is being discussed. One issue with suchlarge bandwidth is that it is challenging to find free 100 MHz ofcontiguous spectrum, due to that radio spectrum a limited resource.

It should be mentioned that LTE-advanced can be viewed as a futurerelease, denoted release-10 (Rel-10) of the LTE standard and since it isan evolution of LTE, backward compatibility is important so thatLTE-advanced can be deployed in spectrum already occupied by LTE (e.g.Rel-8). This means that for a LTE user equipment or a LTE terminal, aLTE-advanced capable network can appear as a LTE network.

As mentioned earlier, in LTE-advanced that can support 100 MHz ofbandwidth. This can be performed by aggregating non-continuous spectrum,to create, from e.g. a baseband point of view, a larger systembandwidth. This is also known as carrier-aggregation, where multiplecomponent carriers are aggregated to provide a larger bandwidth. FIG. 1illustrates an example of carrier aggregation which is aggregation ofmultiple component carriers. Each component carrier can appear as an LTEcarrier, while an LTE-advanced terminal (or UE) can exploit the totalaggregated bandwidth. As shown in FIG. 1, each bandwidth of e.g. 20 MHZrepresents one component carrier. The LTE-advanced system can thereforebe viewed as a multi-carrier system. Aggregation of multiple componentcarriers (CC) allows large bandwidth for supporting data rates of 1 Gb/sor even above, which corresponds to the throughput requirement for the(international mobile telecommunications) IMT-advanced system.Furthermore, such a scenario makes it also possible to adapt thespectrum parts to the current situation and geographical position makingsuch a solution very flexible. To an LTE Rel-8 UE each CC (e.g. of 20Mhz bandwidth), as shown in FIG. 1, will appear as an LTE carrier, whilean LTE-advanced UE can use all 5 CCs i.e. the total aggregated bandwidth(e.g. 100 MHz) such as the one shown in FIG. 1. Thus, a Rel-8 LTE can beviewed as a single carrier system whereas a LTE-advance (Rel-10) can beviewed as a multi-carrier system.

In LTE, a UE's first access to the system is performed by means of a socalled random access (RA) procedure. The objectives of the RA proceduremay include: initial access; connection re-establishment, handover;scheduling request (request for radio resources); timingsynchronization, and the like. The radio network nodes generally controlthe behavior of the UE. As an example, uplink transmission parameterslike frequency, timing and power are regulated via downlink controlsignalling from the radio base station (known in LTE as eNB or eNodeB)to the UE. For the uplink (UL) frequency and power estimate parameters,a UE can derive those parameters from one or several downlink (control)signals.

The RA procedure can be classified into a contention-based random accessprocedure and a contention-free (or non-contention-based) random accessprocedure. The RA procedure is disclosed in the 3GPP technicalspecifications 3GPP TS 36.321 entitled: “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC)protocol specification (Release 8)”

As an example, for an initial access to the network, the RA procedure iscontention-based in which case the UE follows a contention resolutionprocedure. A contention resolution allows a UE to determine whether ornot resources granted by the network as a response to the RA areintended to the UE. Contention resolution is important because multipleUEs may attempt to access the system using the same common resource(e.g. physical random access channel (PRACH) and the same randomlyselected preamble.

It should be noted that for the contention-based random accessprocedure, a plurality (or a set) of non-dedicated random accesspreambles are assigned per cell (i.e. to a eNB). This set is primarilyused when there is UE-originated data and the UE has to establish aconnection and an adequate uplink timing relation with the networkthrough the RA procedure. When performing contention-based randomaccess, the UE arbitrarily selects a preamble from the set as thenon-dedicated random access preamble. This is known as UE initiatedrandom access (supported in LTE). Thus for contention-based randomaccess, the network (or the eNB) is not (immediately) aware of which UEselected which preamble. A drawback with this is that multiple UEs mayin fact select the same preamble and they may attempt to access thenetwork (or access the eNodeB) at the same time. Therefore thecontention resolution mechanism is important.

Prior to accessing the single carrier system using the RA procedure, theUE needs the available set of PRACH resources for the transmission ofthe RA Preamble; the UE may acquire these parameters by reading thebroadcasted system information of the cell or these parameters may beincluded in the message sent by the source eNB in case of handover.

For accessing the system when the UE is already known to the network, acontention-free RA is also possible. For performing contention-freerandom access, there is also defined a set of RA preambles assigned percell (i.e. to a eNB). These preambles are known as dedicated RApreambles. The dedicated preamble is an example of a temporary uniqueidentity to be used on the common resource, and is allocated to the UEprior to the access.

FIG. 2 illustrates a simplified flow diagram depicting steps used in aRA procedure in case of initial access (e.g. contention-based).

The contention-based RA procedure consists of four steps. In the firststep, the UE transmits MSG1 which consists of a randomly selectedpreamble; the UE will later, on a resource calculated based in the PRACHresource used for the transmission of the preamble, monitor for a (RA)response (i.e. MSG2) from the network, which response includes thetransmitted preamble.

In the second step, the UE receives and successfully decodes MSG2containing a preamble that matches the one sent in the previous step.MSG2 includes a Temporary C-RNTI i.e. a temporary identity for the UEwhich purpose is to identify the UE when resolving contention and agrant for a dedicated transmission on UL-SCH (uplink shared channel).

In the third step, the UE transmits MSG3 which contains a MAC SDU filledwith data from upper layers that triggered the initial access to thesystem. Once MSG3 is sent, the UE monitors the PDCCH (physical downlinkcontrol channel) for the Temporary C-RNTI received in the second step.

In the fourth step, the UE has successfully decoded the PDCCH for theTemporary C-RNTI; if the received MAC SDU contains a copy of the MAC SDU(media access control service data unit) transmitted in MSG3, the UEassumes that it won the contention and continues dedicated transmissionsusing the Temporary C-RNTI as its C-RNTI.

The RA procedure (contention based or not) can also be used when the UEis known from the network (i.e. when the UE has a valid C-RNTI) for thepurpose of gaining access to uplink resources and/or uplink timingsynchronization, in case the UE is not assigned dedicated resources one.g. the PUCCH (the physical uplink control channel) for transmission ofa scheduling request.

Furthermore, the RA procedure can be initiated by an PDCCH ordertriggered by the eNB. The eNB can send a PDCCH consistent with a PDCCHorder masked with a C-RNTI and as the UE receives the PDCCHtransmission, the UE initiates a RA procedure. The PDCCH order canindicate a RA preamble (or the identity of the preamble) and resourceinformation i.e. PRACH information.

The RA procedure is also used when a UE performs a handover (HO) from aserving eNB to a target eNB. In LTE (Rel-8), the HO procedure isdescribed in 3GPP TS 36.331 entitled “Evolved Universal TerrestrialRadio Access (E-UTRA); Radio Resource Control (RRC)”;

In short, the source eNB starts by making a decision to handover the UEbased on some criteria e.g. measurement report(s) received from the UE.Then the source eNB can prepare or setup a target eNB and further makeadditional preparations before transmitting a RRC (radio resourcecontrol) connection reconfiguration with mobility information message(aka HO command) towards the UE. The UE then detaches from the cell thatis served by the source eNB and the UE synchronizes to the new cellserved by the target eNB. Thereafter, the UE performs a RA in the newcell. The RA can be contention-free if the preamble was received in theHO command, else the previously described 4 steps for contention-basedare used to perform the RA. Thereafter, the UE transmits RRC connectionreconfiguration complete message. Note that additional steps areperformed which are not explicitly described above.

Note also that at HO, it is possible for the target eNB to signal adedicated preamble in the HO command to the UE which can be transmittedvia the source eNB prior to the change of the serving cell. This can beperformed to speed up the HO procedure by the UE in the target cell andto speed up network-initiated access by the UE in the serving cell.

As mentioned before, LTE (Rel-8) is a single carrier system in which a“cell” can correspond to only one component carrier (CC). The RAprocedure, due to an ordered RA or due to a HO, is important forenabling a UE to successfully access resources and commencetransmissions. Also mentioned earlier is that in LTE, a number ofpreambles can be reserved for dedicated use in a given cell (or in agiven CC) and the dedicated preambles may be transmitted in the samePRACH resources as random preambles. Thus in single-carrier LTE, a UEcan access PRACH resources in the cell (CC) for which the dedicatedpreamble is valid for the UE.

However, a multi-carrier system (e.g. LTE-advanced) can be defined usingeither a plurality of single carrier cells or as a single cell with aplurality of CCs (the latter will be assumed from this point on, howevernot limiting the applicability of the invention herein). In amulti-carrier system, to acquire system information, the UE may berequired to first monitor the broadcasted system information in one ofthe carriers to determine the structure of the multi-carrier cell. TheUE could then either perform random access immediately using the PRACHresources of this carrier (if allowed by the system configuration), oralternatively monitor system information on one or more of the othercarriers to locate other allowed PRACH resources (if any). A carriercould also broadcast information on location of PRACH resources in otherCCs, which would however represent some overhead to the system.

From the multi-carrier capable UE's perspective, the process of findingthe first allowed and suitable PRACH resource and opportunity mayrepresent considerable processing and additional latency in accessingthe system and commencing transmissions. From the network's perspective,broadcasting in one or more CCs system information containing adescription of the PRACH resources available in other carriersrepresents additional complexity and overhead. In addition, the networkhas little control over what resource the UE will use and thus itbecomes a challenge to efficiently manage the system resource related toPRACH.

Therefore, because in a multi-carrier system several CCs are defined percell, where PRACH resources may or may not be allocated and whenallocated may be offset in time between each CC, a HO procedure and/or aPDCCH-ordered RA of a UE in such a multi-carrier cell can take long timecompared to single-carrier system thereby introducing/increasing accessdelays or access latency e.g. HO latency and RA-ordered latency.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the exemplary embodiments of the presentinvention to address the above mentioned problems and to provideimproved methods and apparatuses for resource management in amulti-carrier system wherein a plurality of CCs are defined per cell(e.g. in LTE advanced system). The exemplary embodiments of the presentinvention relate to scenarios during a cell preparation for a HOprocedure from a cell to another cell and/or due to an ordered RA.

According to a an aspect of exemplary embodiments of the presentinvention, the above stated problem is solved by means of a method in aradio base station (e.g. eNodeB or eNB) for resource management in amulti-carrier system wherein a plurality of component carriers aredefined per cell. The method comprises: assembling, in said radio basestation, a message comprising information on the structure of themulti-carrier cell served by the radio base station. The informationincluding one or more CCs used in the cell that is/are available for theUE for performing initial access in the cell. The method furthercomprises, transmitting said message to the UE and indicating to the UEto what resource(s) the UE is to use for random access in the cell.

According to another aspect of exemplary embodiments of the presentinvention, the above stated problem is solved by means of a radio basestation for resource management in a multi-carrier system wherein aplurality of component carriers are defined per cell. The radio basestation comprises means (e.g. an assembler in a processing unit)configured to assemble a message comprising information on the structureof the multi-carrier cell served by the radio base station. Theinformation including one or more CCs used in the cell that is/areavailable for the UE to perform initial access in the cell. The radiobase station further comprises transmitting means (e.g. one or moretransmitters/receivers or transceivers TX/RX) that is configured totransmit the assembled message to the UE and to indicate to said UE towhat resource(s) the UE is to use for random access in the cell.

According to a further aspect of exemplary embodiments of the presentinvention, the above stated problem is solved by means of a method in auser equipment (UE) that is capable in operating in a multi-carriersystem comprising a radio base station serving a cell wherein aplurality of carrier components are defined. The method comprising,receiving a message from the radio base station, said message beingassembled by the radio base station and comprises information includingone or more CCs used in the cell that is/are available to the UE forperforming initial access in the cell. The method further comprises,determining, based on the received information, to what resource(s) touse in the cell; selecting one or more resources and performing a randomaccess in the cell based in the determined information.

According to a yet another aspect of exemplary embodiments of thepresent invention, the above stated problem is solved by means of a userequipment (UE) that is capable in operating in a multi-carrier systemcomprising a radio base station serving a cell wherein a plurality ofcarrier components are defined. The UE comprises receiving means (e.g. atransceiver) that is configured to receive a message from the radio basestation, said message being assembled by the radio base station andcomprises information including one or more CCs used in the cell thatis/are available for the UE to perform initial access in the cell. TheUE further comprises determining means configured to determine, based onthe received information, to what resource(s) to use in the cell. The UEis further configured to select one or more resources and furtherconfigured to perform a random access in the cell based on thedetermined information.

An advantage with the present invention is to reduce handover latency ina multi-carrier system.

Another advantage with the present invention is to reduce access delayif the UE is ordered to perform a random access in a multi-carrier cell.

Yet another advantage with the present invention is to enable a radiobase station to control resource load (e.g. PRACH load) betweensingle-carrier capable UEs (e.g. a 3GPP LTE Rel-8/9) and multi-carriercapable UEs (e.g. 3GPP LTE Rel-10 UEs and beyond).

Yet another advantage with present invention is to enable a radio basestation to have means to tradeoff preamble assignment for lower latency(HO or ordered RA).

Yet another advantage with the present invention is to enable a radiobase station to more efficiently allocate resources (e.g. PRACH) withoutnecessarily impacting RA latency in the cell served by the radio basestation.

Yet another advantage with the present invention is that a UE does notneed to tune/read broadcasted system information for all CCs whenaccessing the multi-carrier cell upon HO and/or upon an ordered RA.

Still other objects and features of the exemplary embodiments of thepresent invention will become apparent from the following detaileddescription in conjunction with the accompanying drawings, attention tobe called to the fact, however, that the following drawings areillustrative only, and that various modifications and changes may bemade in the specific embodiments illustrated. It should further beunderstood that the drawings are not necessarily drawn to scale andthat, unless otherwise indicated, they are merely intended toconceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In the following section, the invention will be described with referenceto exemplary embodiments illustrated in the figures, in which:

FIG. 1 is a diagram illustrating an example of aggregation of multiplecomponent carriers in LTE.

FIG. 2 is a simplified diagram illustrating four steps in a RA procedurein case of initial access.

FIG. 3 is a simplified diagram illustrating an exemplary wirelesstelecommunications system wherein exemplary embodiments of the presentinvention can be applied.

FIG. 4 is a diagram illustrating a flowchart of a method performed, in aradio base station (eNB), according to exemplary embodiments of thepresent invention.

FIG. 5 is a diagram illustrating a flowchart of a method, performed in auser equipment (UE) according to exemplary embodiments of the presentinvention.

FIG. 6 illustrates a block diagram of an exemplary radio base station(eNB) according to embodiments of the present invention.

FIG. 7 illustrates a block diagram of an exemplary user equipment (UE)according to exemplary embodiments of the present invention.

FIG. 8 illustrates a block diagram of an exemplary MME/GW.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, scenarios, techniques, etc. in order to provide thoroughunderstanding of the present invention. However, the differenceexemplary embodiments of the present invention may be practiced in otherembodiments that depart from these specific details.

The different exemplary embodiments of the present invention aredescribed herein by way of reference to particular example scenarios. Inparticular, the invention is described in a non-limiting general contextin relation to resource management in a multi-carrier system that isbased on the third generation (3G) long term evolution (LTE) concept(e.g. LTE-advanced) wherein a plurality of component carriers (CC) canbe defined per cell. It should be noted that the present invention isnot restricted to 3G LTE-advanced but can be applicable in otherwireless multi-carrier systems wherein random access procedures inconnection with handover and/or a PDCCH-ordered random access can beperformed.

Referring to FIG. 3, there is illustrated a block diagram of anexemplary wireless telecommunications network system in which thedifferent exemplary embodiment of the present invention may be applied.Note that the system depicted in FIG. 3 only shows transceivers or nodesthat are necessary for understanding the different exemplary embodimentsof the present invention. As shown, the system, which can be representedby a LTE system (LTE Rel-8 and/or Rel-10), comprises a number of userequipments UE 30 (only one is shown), and apparatuses acting as radiobase stations (eNBs) 31, 32 and 33. One of the functions of the eNodeBsis to control traffic to and from UEs in a cell. A UE is suitable to beused as a mobile phone, a wireless terminal, a laptop, a personalcomputer, a personal digital assistant, a voice over internet protocol(VoIP) capable phone or any other 3GPP LTE capable equipment. Traffic,over a radio link, from a eNodeB to a UE is referred to as downlink (DL)traffic and traffic, over a radio link, from the UE to a eNB is referredto as uplink (UL) traffic. Note that in FIG. 3, the number of UEs andeNBs is only illustrative and the embodiments of the present inventionare not restricted to any particular number of UEs and/or number ofeNBs. The figure also depicts a core network 34 to which the eNBs 31, 32and 33 can be connected.

In FIG. 3, it is assumed that eNB 31 is serving a single-carrier celli.e. eNB 31 can represent a Rel-8 LTE eNB. eNB 32 can represent aLTE-advanced eNB that can serve a multi-carrier cell wherein a pluralityof CCs can be defined. eNB 33 can be a LTE eNB or a LTE-advanced eNB.Furthermore, a number of dedicated preambles can be reserved fordedicated use in a given cell to a eNB, and dedicated preambles aretransmitted in the same PRACH resources as random preambles. The singlecarrier cell (not shown) that is served by eNB 31, corresponds to oneCC, whereas the multi-carrier cell (not shown) that is e.g. served byeNB 32, corresponds to a plurality of CCs.

It should be noted that in LTE, the setting of random access channel(RACH) parameters may depend on a multitude of factors e.g. the uplinkinter-cell interference (from PUSCH), RACH load (call arrival rate, HOrate, tracking area update, and traffic pattern and population under thecell coverage as it affects the UL synchronization states and hence theneed to use random access), the cubic metric of the preambles allocatedto a cell, whether the cell is in high-speed mode or not, and UL and DLimbalances. As an example, an automatic RACH (optimization) function maymonitor the prevailing conditions, e.g., changes on RACH load, uplinkinterference, and may determine and update the appropriate parameterssuch that requirements on performance are satisfied.

Furthermore, optimal RACH performance is key to obtain high coverage andlow delays, e.g., call setup delays, data resuming delays from the ULunsynchronized state, and handover delays. A poorly configured RACH mayresult in low preamble detection probability and low coverage. Furtherif RACH is not dimensioned according to prevailing traffic load, thenthis may result in unnecessarily high access delays. Since random accessis the first step taken in order to commence services, it is importantthat the performance of RACH is satisfactory. RACH performance will havean effect on multiple features and characteristics that are necessaryfrom early network operation, e.g., cell coverage, access delay, andhandover performance. RACH optimization aims at setting the optimum RACHcoverage and random access delay in early network deployment. Forexample, the coverage of a cell is limited by the RACH coverage.Further, RACH parameters need to be updated if there areparameter/configuration changes due to eNB SON (self-organizednetwork)/RRM (radio resource management) functions and/or networkconfiguration setting, e.g. antenna tilting, transmission power settingsand handover threshold. As such, the ability to auto tune the RACHcapacity and coverage would likely be a precondition, and seemsessential to enabling auto tuning of other parameters, since the RACHperformance is probably affected by execution of other SON functions.

It should be noted that for LTE-advanced, 3GPP has discussed that itshall be possible for both single carrier and multi-carrier capable UEsto operate in each CC independently.

Given the assumptions that (1) preambles for PRACH are consequentlyexpected to be handled by the network in a similar manner as for LTERel-8 and that (2) the validity of dedicated preambles are expected toremain per CC, it may be useful to consider the multi-carrier structureof a cell in relation to the use of common resources e.g. PRAHresources.

This may have the following implications for a UE supportingmulti-carriers:

-   -   the UE would e.g. access PRACH resources in the CC for which the        dedicated preamble is valid for that UE;    -   the UE, for which the network intends to reduce access latency        by providing means for this UE to perform a contention-free        access RA, maybe cannot use a PRACH opportunity in a specific CC        unless the UE has a dedicated preamble for that CC.

Furthermore, considering that for a multi-carrier cell the network couldconfigure PRACH resources with different time locations in different CCsto e.g. improve RA latency for UEs supporting multi-carrier whilekeeping the overall capacity and resource allocation at the same levelof efficiency as for a single carrier system, efficient handling ofallocation of dedicated preambles is important.

Assume for example that UE 30 in FIG. 3 is served by eNB 31 and is toperform a HO to the multi-carrier cell that is served by eNB 32. Thus inthis case eNB 31 is a source eNB and eNB 32 is a target eNB. Accordingto an exemplary embodiment of the present invention, eNB 32 isconfigured to construct/assemble a message corresponding to a HO commandand to transmit this to the UE 30 transparently via the source eNB 31.The message may comprise information on the structure of themulti-carrier cell. The information may include e.g. a number of CCs, alist of one or more allowed CCs for PRACH access which may comprise acorresponding dedicated preamble, and may further include a PRACHconfiguration for the CC(s) in the list.

For example, to reduce latency at HO using a contention-free RAprocedure, the HO command may include the cell carrier structure, one ormore dedicated preamble(s) together with an indication of what CC thepreamble is valid. The received information indicating to what resourcesthe UE should use in the multi-carrier cell, can be used by the UE todetermine in what CC it can (earliest) perform RA and to select theavailable (e.g. first available) PRACH resource for the RA in that CC ofthe target cell served by the target eNB 32.

According to an exemplary embodiment of the present invention, theresource management function/method in the eNB 32 is thus configured todetermine what PRACH resources and CC combination(s) a UE can use forthe initial access to the cell.

It should be noted that the exemplary embodiments of the presentinvention are not restricted to HO i.e. the above described resourcemanagement method/function in the eNB is also applicable to aPDCCH-ordered RA ordered by e.g. a serving eNB to the UE.

As mentioned above, the resource management function/method in the eNBis configured to determine e.g.:

-   -   what CC (or subset of CCs) the UE shall use for initial access        in the target cell (for contention-based or contention-free        random access),        This can, for example, be based on: PRACH configuration (timing,        resource allocation) in each CC, or PRACH load in each CC;    -   what dedicated preamble(s) to use for the initial random access        in the target cell for the CC (or for the subset of CCs) in        which the UE is allowed to perform the initial access.

The message (HO command or RA-order) assembled by the eNB andtransmitted to the UE by the serving eNB or by the source eNB (in caseof HO) or by the target eNB via the source eNB (in case of HO) or by thetarget eNB, in order to direct the UE or to steer the UE or to indicateto the UE the intended PRACH resource(s), may thus comprise, inaccordance with an exemplary embodiment of the present invention:

-   -   information on the structure of the multi-carrier cell, which        comprises one or more CCs (e.g. a number of CCs) and/or the        identity of the CC(s) (CCids), and/or the carrier frequency(ies)        (carrierFreq), and/or the bandwidth per carrier        (carrierBandwidth), and/or one or several timers e.g. the timer        T304, etc.

In accordance with an exemplary embodiment of the present invention, theinformation may further comprise one or more default uplink componentcarrier(s) for subsequent PRACH access (e.g. one or more of the CCid(s)above). The information may further comprise one or more defaultdownlink component carrier(s) (e.g. one or more of the CCid(s) above)associated with an uplink component carrier for subsequent PRACH access.The information may further comprise one or more default uplink-downlinkcomponent carrier pair(s) (e.g., identified by one or more of theCCid(s) above) for subsequent PRACH access on the uplink componentcarrier. The information may further include a dedicated preamble foreach of the CCs for which the UE is allowed to use PRACH resources (e.g.RACH-ConfigDedicated with ra-PreambleIndex and ra-PRACH-MaskIndex forone or more of the CCid(s) above). The information may further compriseadditional information not explicitly described above i.e. the exemplaryembodiments of the present invention are not restricted to the abovedescribed information.

As mentioned before, when the UE receives said information in the HOcommand or in the PDCCH-RA order, it determines in what CC it can e.g.earliest perform RA and it can then select the first available resourcefor performing the random access in that CC of the cell (e.g. targetcell).

This way, the UE does not need to tune/read the broadcasted systeminformation for all CCs when accessing the multi-carrier cell upon HO orupon ordered RA thereby reducing HO latency and delay when performingrandom access. In addition, the tradeoff between overall PRACH capacityand latency performance is improved.

Accordance to another exemplary embodiment of the present invention aserving (or a source) eNB can send/signal the HO command message withonly one CC frequency and then the UE can read system information onthat CC frequency in order to gain or listen to the multi-cell structureinformation and then the UE can peak one of the carriers e.g. randomlyor selectively, in order to determine what PRACH resource to use in thatcarrier and then perform the random access. The UE may also read systeminformation on the carrier frequency in the received message to gain inthat carrier and perform random access. As mentioned earlier, theexemplary embodiments of the present invention are also applicable for aRA-order. It should be noted that for a RA-order or for a HO command,the indicated cell for random access in said order or command can beindicated to become the serving cell using e.g. a cell ID. As anexample, if we assume that one cell corresponds to one CC and the othercarriers can serve as resources, then the UE can see one of thesecarriers as the serving cell and this could also be indicated (usinge.g. CCid) in the command or order. Thus, by signalling one CC as the CCto perform random access for the cell, one could also signal one CC asbeing the serving cell. The signaled CC can be the same as the CC usedto perform random access. In this case, the CC becomes the serving cellfrom the UE's perspective. On the other hand, if we assume that one cellcorresponds to multiple CCs then one CC can be signaled (in the HOcommand or RA-order) as the CC to perform random access in the cell andone could also signal one CC as the anchor for the serving cell. Thus, aproperty of a CC can be sent in the HO command or RA order for thepurpose of initial access. It should be noted that the informationregarding the structure of the cell can comprise information about oneCC and that additional CCs can be configured later using dedicatedsignalling.

Referring to FIG. 4 there is described a flowchart of a method forresource management aimed to be performed/implemented in radio basestation e.g. a eNB or a eNodeB capable in operating in a multi-carriersystem wherein cells are allocated a plurality of CCs. As shown, themain steps comprise:

-   (401) assembling a message (e.g. HO command message and/or a    RA-order) comprising information on the structure of the    multi-carrier cell served by the radio base station. The information    comprising one or more CCs used in the cell that a UE can use for    initial access in the cell.-   (402) transmitting said message to the UE and-   (403) indicating to said UE to what resource(s) the UE is to use for    random access in the cell.

Details on what information can be included in the message from the eNBto the UE have been previously described and are therefore notunnecessarily repeated again.

Referring to FIG. 5 there is described a flowchart of a method aimed tobe performed/implemented in UE e.g. capable in operating in amulti-carrier system wherein cells are allocated a plurality of CCs. Asshown, the main steps comprise:

-   (501) receiving a message (e.g. a HO command message and/or a    RA-order) that has been assembled by a eNB, the message including    one or more CCs used in the cell that a UE can use for initial    access in the cell.-   (502) determining, based on the received information, to what    resource(s) to use in the cell.-   (503) selecting one or several resources (e.g. PRACH resource(s))-   (504) performing a random access in the cell based on the determined    information.

Referring to FIG. 6 there is illustrated a block diagram of an exemplaryradio base station 600 (e.g. eNB or eNodeB). Exemplary components of eNB600 are shown. As illustrated, eNB 600 may include antennas 610,transceivers 620, a processing system 630, and an interface 640.Antennas 610 may include one or more directional and/or omni-directionalantennas. Transceivers 620 may be associated with antennas 610 andinclude transceiver circuitry for transmitting and/or receiving symbolsequences in a network via antennas 610. Processing system 630 maycontrol the operation of eNB 600. Processing system 630 may also processinformation received via transceivers 620 and interface 640. Asillustrated, processing system 630 may include processing logic 632 anda memory 634. It will be appreciated that processing system 630 mayinclude additional and/or different components than illustrated in FIG.6. Processing logic 632 may include a processor, microprocessor, anASIC, FPGA, or the like. Processing logic 632 may process informationreceived via transceivers 620 and interface 640. The processing logic632 may also act as an assembler which is configured, in accordance withexemplary embodiments of the present invention, to assemble a messagecomprising information on the structure of the multi-carrier cell servedby eNB 600. The information comprising one or more CCs used in the cellthat a UE can use for initial access in the cell. The eNB 600transceiver 620 (e.g. one or more transmitters/receivers or transceiversTX/RX in combination with antenna(s)) is configured to transmit theassembled message to the UE and to indicate to said UE to whatresource(s) the UE is to use for random access in the cell.

The processing may include, for example, data conversion, forward errorcorrection (FEC), rate adaptation, Wideband Code Division MultipleAccess (WCDMA) spreading/dispreading, and quadrature phase shift keying(QPSK) modulation etc. In addition, processing logic 632 may generatecontrol messages and/or data messages and cause those control messagesand/or data messages to be transmitted via transceivers 620 and/orinterface 640. Processing logic 632 may also process control messagesand/or data messages received from transceivers 620 and/or interface640. Memory 634 may include a RAM, a ROM, and/or another type of memoryto store data and instructions that may be used by processing logic 632.

Interface 640 may include one or more line cards that allow eNB 600 totransmit data to and receive data from other devices over wired and/orwireless connections. As illustrated, interface 640 may include an S1interface 642 that allows eNB 600 to communicate, for example, with aMME/GW (mobility management entity/gateway), and an X2 interface 644that allows eNB 600 to communicate with another eNB. eNB 600 may performcertain operations in response to processing logic 632 executingsoftware instructions contained in a computer-readable medium, such asmemory 634. A computer-readable medium may be defined as one or morephysical and/or logical memory devices. The software instructions may beread into memory 634 from another computer-readable medium or fromanother device via interface 640. The software instructions contained inmemory 634 may cause processing logic 632 to perform processes describedherein. Alternatively, hardwired circuitry may be used in place of or incombination with software instructions to implementprocesses/function/method described herein. Thus, embodiments describedherein are not limited to any specific combination of hardware circuitryand software.

Although FIG. 6 shows exemplary components of eNB 600, in otherimplementations, eNB 600 may contain fewer, different, or additionalcomponents than depicted in FIG. 6. In still other implementations, oneor more components of eNB 600 may perform the tasks described as beingperformed by one or more other components of eNB 600.

Referring to FIG. 7 there is illustrated a diagram of exemplarycomponents of UE 700. As illustrated, UE 700 may include one or severalantennas (only one antenna is shown) 730, a transceiver 705, processinglogic 710, a memory 715, an input device(s) 720, an output device(s)725, and a bus 730. Antenna 730 may include one or more antennas totransmit and/or receive radio frequency (RF) signals over the air.Antenna 730 may, for example, receive RF signals from transceiver 705and transmit the RF signals over the air to an eNB and receive RFsignals over the air from said eNB and provide the RF signals totransceiver 705. Antenna 730 in combination with transceiver 705 istherefore configured to receive, as previously described, a message(e.g. HO command message and/or a RA-order) that has been assembled by aeNB, the message comprising one or more CCs used in of the multi-carriercell served by a radio base station that the UE can use for initialaccess in the cell.

Transceiver 705 may include, for example, a transmitter that may convertbaseband signals from processing logic 710 to RF signals and/or areceiver that may convert RF signals to baseband signals. Alternatively,transceiver 705 may include a transceiver to perform functions of both atransmitter and a receiver. Transceiver 705 may connect to antenna 730for transmission and/or reception of the RF signals.

Processing logic 710 may include a processor, microprocessor, anapplication specific integrated circuit (ASIC), field programmable gatearray (FPGA), or the like. Processing logic 710 may control operation ofUE 700 and its components. The processing unit 710 may therefore,determine based on the information received in the HO command or in theRA-order command to what resource(s) to use in the cell. As previouslydescribed, the received information comprises on one or more CCs used inthe cell that is/are available for the UE to or the informationcomprises information on the structure of the multi-carrier cellincluding the one or more CCs. The processing logic 710 may also beresponsible in selecting one or several resources (e.g. PRACHresource(s)). The UE 700 is also configured to performing a randomaccess in the cell based on the determined information.

Referring to FIG. 7, the UE further comprises a memory 715 which mayinclude a random access memory (RAM), a read only memory (ROM), and/oranother type of memory to store data and instructions that may be usedby processing logic 710. Input device(s) 720 may include mechanisms forentry of data into UE 700. For example, input device(s) 720 may includeinput mechanisms, such as microphone, input elements, display, etc.Output device(s) 725 may include mechanisms for outputting data inaudio, video and/or hard copy format. For example, output device(s) 725may include speaker, display, etc. Bus 730 may interconnect the variouscomponents of UE 700 to permit the components to communicate with oneanother.

Although FIG. 7 shows exemplary components of UE 700, in otherimplementations, UE 700 may contain fewer, different, or additionalcomponents than depicted in FIG. 7. In still other implementations, oneor more components of UE 700 may perform the tasks described as beingperformed by one or more other components of UE 700.

As mentioned earlier, the eNB can communicate with a MME/GW. FIG. 8 is adiagram of exemplary components of MME/GW 800 capable in communicatingwith e.g. eNB 600 of FIG. 6. As illustrated, MME/GW 800 may include aprocessing system 810 and an interface 820. Processing system 810 maycontrol the operation of MME/GW 800. Processing system 810 may alsoprocess information received via interface 820. As illustrated,processing system 810 may include processing logic 812 and a memory 814.It will be appreciated that processing system 810 may include additionaland/or different components than illustrated in FIG. 8.

Processing logic 812 may include a processor, microprocessor, an ASIC,FPGA, or the like. Processing logic 812 may process information receivedvia interface 820. In addition, processing logic 812 may generatecontrol messages and/or data messages and cause those control messagesand/or data messages to be transmitted via interface 820. Processinglogic 812 may also process control messages and/or data messagesreceived from interface 820. Memory 814 may include a RAM, a ROM, and/oranother type of memory to store data and instructions that may be usedby processing logic 812.

Interface 820 may include one or more line cards that allow MME/GW 800to transmit data to and receive data from other devices over wiredand/or wireless connections. As illustrated, interface 820 may includean S1 interface 822 that allows MME/GW 800 to communicate, for example,with eNB 600. It will be appreciated that interface 820 may includeadditional interfaces than illustrated in FIG. 8. For example, interface820 may include an interface for communicating with another network,such as a PDN (packet data network).

MME/GW 800 may perform certain operations in response to processinglogic 812 executing software instructions contained in acomputer-readable medium, such as memory 814. The software instructionsmay be read into memory 814 from another computer-readable medium orfrom another device via interface 820. The software instructionscontained in memory 814 may cause processing logic 812 to performprocesses described herein. Alternatively, hardwired circuitry may beused in place of or in combination with software instructions toimplement processes described herein.

It should be noted that the exemplary embodiments described herein arenot limited to any specific combination of hardware circuitry andsoftware.

The present invention and its embodiments can be realized in many ways.For example, one embodiment of the present invention includes acomputer-readable medium having instructions stored thereon that areexecutable by a radio base station (e.g. eNodeB or eNB) and/or a UE of atelecommunications system. The instructions executable by the radio basestation and/or the UE and stored on a computer-readable medium performthe method steps of the present invention as previously described.

What is claimed:
 1. A radio base station operable in a multi-carriersystem comprising a plurality of component carriers (CCs), comprising: aprocessing unit; and a memory including computer program code, whereinthe processing unit, the memory, and the computer program code arecollectively configured to: assemble a message including information onthe plurality of CCs, of which only one CC is identified along with adedicated preamble for a physical random access channel (PRACH) resourcewithin the CC for random access within the multi-carrier system; andprovide the message and an indication of the PRACH resource to direct auser equipment to use the dedicated preamble for the PRACH resourcewithin the CC to perform the random access within the multi-carriersystem.
 2. The radio base station according to claim 1 wherein themessage comprises an indicator that the dedicated preamble is valid withrespect to the CC.
 3. The radio base station according to claim 1wherein the message comprises a PRACH configuration and/or a PRACH loadwith respect to the CC.
 4. The radio base station according to claim 1wherein the message comprises an identity (CCid) of the CC, a carrierfrequency (carrierFreq) for the CC, a bandwidth (carrierBandwidth) forthe CC, and/or at least one timer.
 5. The radio base station accordingto claim 1 wherein the message identifies another CC of the plurality ofCCs and another dedicated preamble for another PRACH resource within theanother CC to perform a subsequent random access within themulti-carrier system.
 6. The radio base station according to claim 1wherein the processing unit, the memory, and the computer program codeare collectively configured to provide the message and the indication ofthe PRACH resource to direct the user equipment to use the dedicatedpreamble for the PRACH resource within the CC to perform initial randomaccess within the multi-carrier system.
 7. The radio base stationaccording to claim 1 wherein the PRACH resource comprises time-frequencyresources within the CC to perform the random access within themulti-carrier system.
 8. The radio base station according to claim 1wherein the message is part of a handover command to prepare for ahandover procedure or part of a physical downlink control channel(PDCCH) random access order for the user equipment.
 9. A methodperformed by a radio base station in a multi-carrier system comprising aplurality of component carriers (CCs), comprising: assembling a messageincluding information on the plurality of CCs, of which only one CC isidentified along with a dedicated preamble for a physical random accesschannel (PRACH) resource within the CC for random access within themulti-carrier system; and providing the message and an indication of thePRACH resource to direct a user equipment to use the dedicated preamblefor the PRACH resource within the CC to perform the random access withinthe multi-carrier system.
 10. The method according to claim 9 whereinthe message comprises an indicator that the dedicated preamble is validwith respect to the CC.
 11. The method according to claim 9 wherein themessage comprises a PRACH configuration and/or a PRACH load with respectto the CC.
 12. The method according to claim 9 wherein the messagecomprises an identity (CCid) of the CC, a carrier frequency(carrierFreq) for the CC, a bandwidth (carrierBandwidth) for the CC,and/or at least one timer.
 13. The method according to claim 9 whereinthe message identifies another CC of the plurality of CCs and anotherdedicated preamble for another PRACH resource within the another CC toperform a subsequent random access within the multi-carrier system. 14.The method according to claim 9 wherein the providing comprisesproviding the message and the indication of the PRACH resource to directthe user equipment to use the dedicated preamble for the PRACH resourcewithin the CC to perform initial random access within the multi-carriersystem.
 15. The method according to claim 9 wherein the PRACH resourcecomprises time-frequency resources within the CC to perform the randomaccess within the multi-carrier system.
 16. The method according toclaim 9 wherein the message is part of a handover command to prepare fora handover procedure or part of a physical downlink control channel(PDCCH) random access order for the user equipment.
 17. A user equipmentoperable in a multi-carrier system comprising a plurality of componentcarriers (CCs), comprising: a processing unit; and a memory includingcomputer program code, wherein the processing unit, the memory, and thecomputer program code are collectively configured to: receive a messageincluding information on the plurality of CCs, of which only one CC isidentified along with a dedicated preamble for a physical random accesschannel (PRACH) resource within the CC for random access within themulti-carrier system; and perform the random access within themulti-carrier system using the PRACH resource and the dedicated preamblefor the PRACH resource within the CC.
 18. The user equipment accordingto claim 17 wherein the message comprises an indicator that thededicated preamble is valid with respect to the CC.
 19. The userequipment according to claim 17 wherein the processing unit, the memory,and the computer program code are collectively configured to performinitial random access within the multi-carrier system using the PRACHresource and the dedicated preamble for the PRACH resource within theCC.
 20. The user equipment according to claim 17 wherein the messagecomprises an identity (CCid) of the CC, a carrier frequency(carrierFreq) for the CC, a bandwidth (carrierBandwidth) for the CC,and/or at least one timer.
 21. The user equipment according to claim 17wherein the message identifies another CC of the plurality of CCs andanother dedicated preamble for another PRACH resource within the anotherCC to perform a subsequent random access within the multi-carriersystem.
 22. The user equipment according to claim 17 wherein the PRACHresource comprises time-frequency resources within the CC to perform therandom access within the multi-carrier system.
 23. The user equipmentaccording to claim 17 wherein the message is part of a handover commandto prepare for a handover procedure or part of a physical downlinkcontrol channel (PDCCH) random access order for the user equipment. 24.The user equipment according to claim 17 wherein the processing unit thememory, and the computer program code are collectively configured toread system information with respect to the plurality of CCs to acquireinformation on a structure of the multi-carrier system.
 25. A methodperformed by a user equipment in a multi-carrier system comprising aplurality of component carriers (CCs), comprising: receiving a messageincluding information on the plurality of CCs, of which only one CC isidentified along with a dedicated preamble for a physical random accesschannel (PRACH) resource within the CC for random access within themulti-carrier system; and performing the random access within themulti-carrier system using the PRACH resource and the dedicated preamblefor the PRACH resource within the CC.
 26. The method according to claim25 wherein the message comprises an indicator that the dedicatedpreamble is valid with respect to the CC.
 27. The method according toclaim 25 wherein the message comprises a PRACH configuration and/or aPRACH load with respect to the CC.
 28. The method according to claim 25wherein the performing comprises performing initial random access withinthe multi-carrier system using the PRACH resource and the dedicatedpreamble for the PRACH resource within the CC.
 29. The method accordingto claim 25 wherein the message comprises an identity (CCid) of the CC,a carrier frequency (carrierFreq) for the CC, a bandwidth(carrierBandwidth) for the CC, and/or at least one timer.
 30. The methodaccording to claim 25 wherein the message identifies another CC of theplurality of CCs and another dedicated preamble for another PRACHresource within the another CC to perform a subsequent random accesswithin the multi-carrier system.
 31. The method according to claim 25wherein the PRACH resource comprises time-frequency resources within theCC to perform the random access within the multi-carrier system.
 32. Themethod according to claim 25 wherein the message is part of a handovercommand to prepare for a handover procedure or part of a physicaldownlink control channel (PDCCH) random access order for the userequipment.
 33. The method according to claim 25 further comprisingreading system information with respect to the plurality of CCs toacquire information on a structure of the multi-carrier system.